The present invention is related to the field of laser sources and, more particularly, to fiber lasers using fiber Bragg gratings.
Fiberoptic systems, such as those in the fields of telecommunications, data communications, sensors, instrumentation and the like, require laser sources which are very stable, have high power, i.e., greater than 10 mW, and low noise. This is true for WDM (Wavelength Division Multiplexed) networks, in particular, which demand a large number of narrow linewidth laser sources for signal generation. Since the wavelength of an optical signal is used to direct the signal from its source to its destination, each user typically has a laser source operating at a specific wavelength different from other laser sources. A stable laser source having a fixed wavelength is highly desirable. Furthermore, an emerging standard is the Dense WDM (DWDM) proposed by the ITU, the International Telecommunications Union, in which the separation between communication channels is only 0.8 nm, or 100 GHz in frequency. Thus a light source for such a network must also have a very narrow output linewidth, i.e., the wavelength of the output signal must be concentrated in a very narrow portion of the optical spectrum.
Heretofore, light sources for fiberoptic networks have been mostly semiconductor devices, such as laser diodes, light-emitting diodes, and other semiconductor laser sources. In particular, the semiconductor laser diode has been the standard laser source for its size, cost, and compatibility with optical fibers in fiberoptic networks. However, the conventional semiconductor laser diode has many inherent shortcomings, including low power, spectral instability over changes in temperature, and low fabrication yields which keep costs high. A new type of laser source is a rare-earth doped optical fiber section with wavelength-selective reflectors at the ends of the section to define a lasing cavity. As in the case of the erbium-doped fiber amplifier, a pumping laser supplies energy to the doped fiber section at one, or multiple, wavelengths. The doped fiber section lases at one, or multiple, different output wavelengths. While seemingly compatible with fiberoptic networks, this laser source has a relatively low output power and the advantages of this laser source have yet to be appreciated.
The present invention provides for a novel fiber laser with a very narrow linewidth output with output power greater than that of other fiber lasers. The output of the fiber laser according to the present invention has low noise, minimal relaxation oscillation, good stability over changes in temperature, and very narrow output linewidths. The fiber laser can be arranged into laser sources which are readily adaptable to fiberoptic networks, particularly WDM and DWDM networks.